Thermal energy storage assembly with phase change materials

ABSTRACT

A thermal energy storage assembly includes a first pipe configured to have a heat transfer fluid flow through a bore of the first pipe and a second pipe surrounding the first pipe. A phase change material fills the space between the first pipe and the second pipe, the phase change material storing cold thermal energy from the heat transfer fluid.

BACKGROUND OF THE INVENTION

Embodiments of the invention relate to refrigeration systems and inparticular to a refrigeration system including a phase-change material.

Refrigeration systems compress and circulate a refrigerant throughout aclosed-loop heat transfer fluid circuit to transfer heat to and from aclimate controlled space. In a basic refrigerant system, a heat transferfluid vapor is compressed in a compressor from a lower pressure to ahigher pressure and delivered to a downstream heat rejection heatexchanger, commonly referred to as a condenser. From the condenser,where heat is typically transferred from the heat transfer fluid to anambient environment or to a secondary heat transfer fluid, high-pressurerefrigerant flows to an expansion device where it is expanded to a lowerpressure and temperature and then is routed to an evaporator. In theevaporator, the heat transfer fluid vaporizes and cools the air in theconditioned environment or the secondary heat transfer fluid. From theevaporator, the refrigerant vapor is returned to the compressor.

BRIEF DESCRIPTION OF THE INVENTION

Embodiments of the invention include a thermal energy storage assemblyhaving a first pipe configured to have a heat transfer fluid flowthrough a bore of the first pipe. A second pipe surrounds the firstpipe. A phase change material fills the space between the first pipe andthe second pipe, the phase change material storing thermal energy fromthe heat transfer fluid.

Additional embodiments include a refrigeration system including acooling unit configured to cool a heat transfer fluid and a thermalenergy storage assembly. The thermal energy storage assembly isconfigured to circulate the heat transfer fluid from the cooling unitand back to the cooling unit to refrigerate a compartment. The thermalenergy storage assembly includes a first pipe configured to have theheat transfer fluid flow through a bore of the first pipe and a secondpipe surrounding the first pipe. A phase change material fills the spacebetween the first pipe and the second pipe and stores thermal energyfrom the heat transfer fluid, or releases thermal energy to the heattransfer fluid.

Additional embodiments of the invention include a mobile refrigerationvehicle including a refrigerated compartment having a thermal energystorage assembly attached to at least one wall of the refrigeratedcompartment. The thermal energy storage assembly includes a first pipeconfigured to have the heat transfer fluid flow through a bore of thefirst pipe and a second pipe surrounding the first pipe. A phase changematerial fills the space between the first pipe and the second pipe andstores cold thermal energy from or release cold thermal energy to theheat transfer fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter, which is regarded as the invention, is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1 illustrates a refrigeration system according to an embodiment ofthe invention;

FIG. 2 is a cross-section view of a thermal energy storage assemblyaccording to an embodiment of the invention;

FIG. 3 is a cross-section view of a thermal energy storage assemblyaccording to another embodiment of the invention; and

FIG. 4 illustrates a refrigerated vehicle according to an embodiment ofthe invention.

The detailed description explains embodiments of the invention, togetherwith advantages and features, by way of example with reference to thedrawings.

DETAILED DESCRIPTION OF THE INVENTION

Conventional refrigeration systems for vehicles utilize eutectic platesfilled with mineral salt solutions to provide refrigeration. Embodimentsof the present invention provide refrigeration using a first pipeenclosed within a second pipe, with a phase change material filling thearea between the two pipes. A heat transfer fluid flows within the firstpipe and the phase change material exchanges heat with the heat transferfluid to maintain a target area at a desired temperature.

FIG. 1 illustrates a refrigeration system 100 according to an embodimentof the invention. The system 100 includes a condensing circuit 110, anevaporator assembly 120 and a thermal energy storage assembly 130. Inone embodiment, a compressor 124 heats a refrigerant in a gaseous state,which heats the refrigerant and provides pressure for the refrigerant toflow between the condensing circuit 110 and the evaporator assembly. Thecondensing circuit 110 condenses the hot refrigerant vapor to apressurized moderate temperature liquid. In one embodiment, a fan (notshown) blows air over the condensing circuit 110 to transfer heat fromthe refrigerant to the air, cooling the refrigerant. The pressure of therefrigerant is reduced by an expansion device 123 and the refrigerant isprovided to an evaporator 120. The evaporator 120 uses the cooledrefrigerant to cool a heat transfer fluid that is circulated through thethermal energy storage assembly 130. The evaporator 120 includes arefrigerant circuit 121 and a heat transfer fluid circuit 122. Theevaporator 120 is configured such that it simultaneously cools the heattransfer fluid from the thermal energy storage assembly 130 and the aircirculated by a fan (not shown) between the evaporator 120 and therefrigerated space. The refrigerant circuit 121 may include, forexample, tubes containing the refrigerant that surround tubes carryingthe heat transfer fluid to cool the heat transfer fluid.

The heat transfer fluid is transmitted from the evaporator assembly 120to the thermal energy storage assembly 130. In one embodiment, thethermal energy storage assembly 130 is located in a compartment that isto be refrigerated. For example, in one embodiment, the thermal energystorage assembly 130 is located in the walls of the compartment, or thethermal energy storage assembly 130 may be attached to the walls of thecompartment. Valves 131 and 132 control the flow of the heat transferfluid to and from the thermal energy storage assembly 130. A pump 133may be used to control a rate of flow of the heat transfer fluid to andfrom the thermal energy storage assembly 130. The cooling load splitbetween cooling return air and the heat transfer fluid can be controlledby varying the flow rate of the heat transfer fluid. The pump 133 isturned on when the thermal storage is charged and discharged through theevaporator 120. The cooling of the air from the thermal energy storageassembly 130 can also be done by running the pump 133 to circulate theheat transfer fluid between the thermal energy storage assembly 130 andthe evaporator 120, while the compressor 124 is turned off, or with thecompressor 124 turned on to boost the cooling capacity with the storedcold thermal energy.

FIG. 2 illustrates a thermal energy storage assembly 220 according to anembodiment of the invention. The assembly 220 includes a first pipe 221and a second pipe 222 surrounding the first pipe 221. In one embodiment,the first pipe 221 and the second pipe 222 are co-axial. However,embodiments of the invention encompass any configuration of the firstpipe 221 and the second pipe 222 where the first pipe 221 is locatedwithin the second pipe 222, such as multiple pipes located inside thesecond pipe 222, the first pipe 221 being offset from the center axis ofthe second pipe 222, or any other configuration. The first pipe 221 isconnected to the evaporator assembly 120 of FIG. 1, and the heattransfer fluid flows through the bore 223 of the first pipe 221. Thearea 224 between the first pipe 221 and the second pipe 222 is filledwith a phase change material. The phase change material stores the coldthermal energy from the heat transfer fluid to cool a compartment inwhich the thermal energy storage assembly 220 is located. Alternatively,the cold thermal energy stored in the thermal energy storage assembly220 may be released to the heat transfer fluid which circulates back tothe evaporator to cool the air flowing through the evaporator. Typicalphase change materials include paraffin waxes, fatty acids from naturaloils, or inorganic salt solution.

In the present specification and claims, a phase change material isdefined as a material that has a melting temperature (from solid toliquid) at which it absorbs heat while maintaining a substantiallyconstant temperature. In other words, as the phase change material isheated up from a temperature below the melting temperature to themelting temperature, the temperature of the phase change material risesaccordingly. However, when the phase change material reaches its meltingtemperature, the temperature of the phase change material remainssubstantially the same as it absorbs heat, before all the phase changematerial becomes liquid. Accordingly, the phase change material locatedbetween the first pipe 221 and the second pipe 222 of the presentinvention acts as a robust refrigeration material that is able to absorbheat from an atmosphere that is being cooled, and that may be refreshed,or cooled, by the heat transfer fluid in the bore 223 of the first pipe221.

In embodiments of the invention, the first and second pipes 221 and 222may be made of any material, according to the design considerations ofthe refrigeration system in which the thermal energy storage assembly220 is located. In one embodiment, one or both of the first and secondpipes 221 and 222 is made of metal. In another embodiment, one or bothof the first and second pipes 221 and 222 is made of plastic or anotherpolymer. In addition, while the first and second pipes 221 and 222 areillustrated as having circular cross-sectional shapes, embodiments ofthe invention encompass pipes having any cross-sectional shapes,including squares, ovals, any other geometric shape, or any other shape.

FIG. 2 illustrates a wall panel 210 of a compartment in which thethermal energy storage assembly 220 is located. As illustrated in FIG.2, the thermal energy storage assembly 220 may be exposed to theatmosphere 230 within the compartment. Alternatively, as illustrated inFIG. 3, the thermal energy storage assembly 220 may be sandwichedbetween two wall panels 210 and 215. The area 240 between the wallpanels 210 and 215, and between adjacent spans of the thermal energystorage assembly 220 may be filled with an insulating material. In oneembodiment, the area between the storage assembly 220 and the inner wallpanel 215 includes a material having heat conductivity to facilitatecooling of the wall panel 215 by the thermal energy storage assembly220.

FIG. 4 illustrates a refrigerated vehicle 400 according to an embodimentof the invention. The vehicle 400 includes a refrigeration compartment401 for refrigerating materials within the compartment 401. The vehicle400 may include a condenser and evaporator 402 for cooling a heattransfer fluid flowing through a thermal energy storage assembly 403. Asdiscussed above, the thermal energy storage assembly 403 may be locatedin the walls of the compartment 401, to save space for objects andmaterials within the compartment 401. Alternatively, the thermal energystorage assembly 403 may be attached to the walls of the compartment 401and exposed to an atmosphere in the compartment 401

While the vehicle 400 of FIG. 4 is illustrate with the condenser andevaporator 402 included with the vehicle 400, in one embodiment thevehicle 400 does not include the condenser and evaporator 402. Instead,the vehicle 400 may be disconnected from a condenser and evaporator 402while the vehicle 400 is travelling, and may be periodically connectedto the condenser and evaporator 402 to cause the heat transfer fluid toflow through the thermal energy storage assembly 220.

Embodiments of the present invention include a unique configuration ofan evaporator cooling a load, such as air circulating inside a truck,container or other compartment. The configuration includes charging athermal storage and cooling the compartment air in a parallel mode. Therefrigerant cools the air at the same time cools the heat transfer fluidwhich is circulated to the thermals storage assembly to charge the phasechange materials. In embodiments of the invention, the storedrefrigeration capacity can be discharged to the load either with orwithout the compression unit running, effectively increasing the maximumcapacity for faster pull down.

In one embodiment, some of the circuits of an evaporator coil for a heattransfer fluid flow though to charge/discharge the thermal storage. Thisconfiguration effectively has better thermodynamic efficiency comparedwith a configuration using multiple heat exchangers. In addition, in oneembodiment, the thermal storage (e.g. phase change material) is embeddedin the insulation wall, reducing the cost for insulating an independentstorage container. In one embodiment, plastic materials are used for thestorage devices to eliminate metal corrosion. For example, referring toFIG. 2, the second pipe 222 may be made of plastic. The embedded phasecontrol materials can function as a dynamic insulation, reducing thepeak heat flux and effectively increasing R-value across the insulationwall at around the phase change temperatures.

While the invention has been described in detail in connection with onlya limited number of embodiments, it should be readily understood thatthe invention is not limited to such disclosed embodiments. Rather, theinvention can be modified to incorporate any number of variations,alterations, substitutions or equivalent arrangements not heretoforedescribed, but which are commensurate with the spirit and scope of theinvention. Additionally, while various embodiments of the invention havebeen described, it is to be understood that aspects of the invention mayinclude only some of the described embodiments. Accordingly, theinvention is not to be seen as limited by the foregoing description, butis only limited by the scope of the appended claims.

1. A thermal energy storage assembly, comprising: a first pipeconfigured to have a heat transfer fluid flow through a bore of thefirst pipe; a second pipe surrounding the first pipe; and a phase changematerial filling the space between the first pipe and the second pipe,the phase change material storing thermal energy from the heat transferfluid.
 2. The thermal energy storage assembly of claim 1, wherein thefirst pipe and the second pipe are co-axial.
 3. The thermal energystorage assembly of claim 1, wherein the first pipe is made of metal. 4.The thermal energy storage assembly of claim 1, wherein the phase changematerial is one of paraffinic waxes or fatty acids from natural oils orinorganic salt solutions.
 5. The thermal energy storage assembly ofclaim 1, wherein one of fins and heat transfer material is located inthe space between the first pipe and the second pipe.
 6. A refrigerationsystem, comprising: a cooling unit configured to cool a heat transferfluid; and a thermal energy storage assembly configured to circulate theheat transfer fluid from the cooling unit and back to the cooling unit,the thermal energy storage assembly configured to refrigerate acompartment, the thermal energy storage assembly comprising: a firstpipe configured to have the heat transfer fluid flow through a bore ofthe first pipe; a second pipe surrounding the first pipe; and a phasechange material filling the space between the first pipe and the secondpipe, the phase change material storing thermal energy from the heattransfer fluid.
 7. The refrigeration system of claim 6, wherein thefirst pipe and the second pipe are co-axial.
 8. The refrigeration systemof claim 6, wherein the thermal energy storage assembly is located in awall of the compartment.
 9. The refrigeration system of claim 8, whereinthe thermal energy storage assembly is exposed to an atmosphere in thecompartment.
 10. The refrigeration system of claim 8, wherein thethermal energy storage assembly is sandwiched between two wall panels ofa wall of the compartment, a space between the two wall panels filledwith an insulation material.
 11. The refrigeration system of claim 6,further comprising: a heat transfer fluid transmission system betweenthe cooling unit and the thermal energy storage assembly to transmit theheat transfer fluid between the cooling unit and the thermal energystorage assembly; and a pump located along the heat transfer fluidsystem to increase a flow rate of the heat transfer fluid based on thepump being turned on.
 12. The refrigeration system of claim 11, whereinthe cooling unit includes an evaporator, the heat transfer fluid passesthrough the evaporator to exchange thermal energy with a refrigerant,and the heat transfer fluid flows through the evaporator and exchangesthermal energy with the refrigerant based on the pump being turned on.13. A mobile refrigeration vehicle, comprising: a refrigeratedcompartment having a thermal energy storage assembly attached to atleast one wall of the refrigerated compartment, the thermal energystorage assembly comprising: a first pipe configured to have the heattransfer fluid flow through a bore of the first pipe; a second pipesurrounding the first pipe; and a phase change material filling thespace between the first pipe and the second pipe, the phase changematerial storing thermal energy from the heat transfer fluid.
 14. Themobile refrigeration vehicle of claim 13, wherein the first pipe and thesecond pipe are co-axial.
 15. The mobile refrigeration vehicle of claim13, wherein the thermal energy storage assembly is located in a wall ofthe compartment.
 16. The mobile refrigeration vehicle of claim 15,wherein the thermal energy storage assembly is exposed to an atmospherein the compartment.
 17. The mobile refrigeration vehicle of claim 15,wherein the thermal energy storage assembly is sandwiched between twowall panels of a wall of the compartment, a space between the two wallpanels and between adjacent lengths of the thermal energy storageassembly being filled with an insulation material.